Method and apparatus for dry etching

ABSTRACT

A method and apparatus for dry etching changes at least one of the effective pumping speed of a vacuum chamber and the gas flow rate to alter the processing of an etching pattern side wall of a sample between first and second conditions. The first and second conditions include the presence or absence of a deposit film, or the presence, absence or shape of a taper angle. Various parameters for controlling the first and second conditions are contemplated.

This is continuation application of U.S. Ser. No. 09/480,477, filed Jan.11, 2000, now U.S. Pat. No. 6,136,721, which is a continuationapplication of U.S. Ser. No. 09/063,406, filed Apr. 21, 1998, now U.S.Pat. No. 6,008,133, which is a divisional application of U.S. Ser. No.08/861,600, filed May 22, 1997, now U.S. Pat. No. 5,795,832, which is adivisional application of U.S. Ser. No. 08/570,689, filed Dec. 11, 1995,now U.S. Pat. No. 5,650,038, which is a divisional application of Ser.No. 08/301,388, filed Sep. 7, 1994, now U.S. Pat. No. 5,474,650, whichis a a continuation-in-part application of U.S. patent application Ser.No. 08/176,461, filed Jan. 3, 1994, now U.S. Pat. No. 5,354,418, whichis a divisional application of U.S. patent application Ser. No.08/034,126, filed Mar. 18, 1993, now U.S. Pat. No. 5,318,667, which is acontinuation-in-part application of U.S. patent application Ser. No.07/859,336, filed Mar. 27, 1992, now U.S. Pat. No. 5,242,539, thedisclosures of all of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dry etching method and a dry etchingapparatus, and, more particularly, to a high-speed exhaust dry etchingmethod and apparatus suitable for highly selective, fine anisotropicpatterning on a semiconductor.

2. Description of the Related Art

Anisotropic patterning is important in the fine patterning ofsemiconductor integrated circuits. In particular, dynamic random accessmemories (DRAMs), having a high degree of integration, require ultrafine patterning for etching the gate and storage capacitor of the MOStransistors that constitute a DRAM. Preferably, highly anisotropicpatterning is realized through dry etching.

Recently, to increase the degree of integration on the DRAM, the storagecapacitor has been formed on the MOS transistor. To pattern the storagecapacitor, step etching has been necessary. In highly anisotropicetching, etching residue is produced on the step wall when the etchingstep only performs etching for film thickness. To remove the etchingresidue, overetching is necessary (that is, etching of more than thefilm thickness).

One example of an overetching method is disclosed in Japanese PatentApplication Laid-Open No. 61-61423. As disclosed, a side-wall protectivefilm is formed after the etching step before removing the etchingresidue through isotropic etching. To prevent an underlayer from beingcut during the overetching, the method disclosed in Japanese PatentApplication Laid-Open No. 63-65628 includes highly-selective etchingafter the formation of a side-wall protective film.

Frequently, the gate and storage capacitor of the MOS transistor areformed of polycrystalline silicon, or polycide. A method for etchingpolycrystalline silicon or polycide with a resist mask and chlorine- orbromine-based gas plasma is shown in “26p-ZF-1” and “26p-ZF-4” of the51st Japan Society of Applied Physics Autumn Meeting in 1990.

The method disclosed in Japanese Patent Application Laid-Open No.2-105413 improves the etching anisotropy by changing gases to correspondto the fine patterning. The method realizes a high anisotropy byperiodically changing an etching gas and a depositing gas.

To further improve the degree of element integration, a vertical shapeshould be formed through highly anisotropic etching. However, the sidewall should be tapered by giving an angle to it, depending upon thepatterning condition after etching. An example of tapered etching isgiven in Proceedings of Symposium on Dry Process (1986), page 48, inwhich a depositing gas is added. Further, Japanese Patent ApplicationLaid-Open No. 1-32633 discloses a method for performing tapered etchingby utilizing the substrate temperature to control the side etchingspeed.

Previous techniques for changing to isotropic etching, or periodicallychanging the etching gas and depositing gas during overetching, requirechange of etching gas. Therefore, the throughput decreases because ofthe excessive time to change gases, and the process conditions should beoptimized for each etching gas.

The known method for utilizing a resist mask and chlorine- orbromine-based gas plasma for the etching of polycrystalline siliconproduces reaction products in the mask and etched layer that areactivated in the plasma and reattached to a sample. This deposition fromthe reaction products acts as a side-wall protective film to preventside etching, so that highly anisotropic etching can be performed.However, the amount of the deposition from the reaction products is notconventionally controlled. Therefore, excessive amounts of deposition ofreaction products may produce dust and cause the yield to decrease.

When forming a side-wall protective film, the amount of deposition fromreaction products changes during the etching step. For example becausethe etching speed is not completely constant for a single wafer, andbecause the thickness of an etched layer is not completely uniform, thearea of the etched layer slowly decreases immediately before the etchingstep ends. Accordingly, the amount of reaction product depositiondecreases because the number of reaction products to be produceddecreases. That is, the thickness of the side-wall protective filmdecreases immediately before the etching step ends. As a result, theside-wall protective film becomes thin around the interface between theetched layer and the underlayer. This thin portion of the protectivefilm is subject to breakage, causing abnormal side etching around theinterface.

A similar problem may result from the method disclosed in U.S. Pat. No.5,242,539 to Kumihashi et al. Kumihashi et al disclose a high-speedexhaust dry etching method for improving throughput by increasing thespeed of the etching process, in which the effective exhaust rate is setat 500 liters/second or higher. In this method, reaction products arequickly exhausted from the processing chamber to increase the processingspeed. The reaction products form side-wall protective films to suppressside etching. In this high-speed exhaust dry etching method, however,the side-wall protective film may fail to be formed to a desiredthickness, resulting in side etching, which in turn deteriorates thegeometrical anisotropy. Further, because the high speed exhaust dryetching also increases the etching rate of a mask, there are cases wherea desired selectivity cannot be obtained. For example, where thematerial to be etched consists of two or more layers having differentetch rates, as in a laminated film, and a layer with a low etch rate isetched, the selectivity is degraded.

Also, previous methods for performing tapered etching by adding adeposit gas have resulted in dust production and yield decrease.Controlling the tapered etching by controlling the substrate temperaturehas been difficult to carry out because of the difficulty in stablycontrolling the substrate temperature, and because much time is requiredto adjust the substrate temperature for fine control.

SUMMARY OF THE INVENTION

The present invention has been designed to easily carry out anisotropicetching and overetching. Further, an objective of this invention is tomake the high-speed processing afforded by high-speed exhaust dryetching compatible with anisotropy and selectivity.

In a preferred embodiment, the inventive dry etching method comprisesthe steps of setting a sample in a vacuum chamber, supplying gas to thevacuum chamber and etching the sample with the supplied gas. At leastone of the effective pumping speed of the vacuum chamber and the flowrate of the gas is changed from conditions under which a deposit film isproduced on the etching pattern side wall of the sample, to conditionsunder which a deposit film is not produced on the side wall, or viceversa. The dry etching method may further include a step of periodicallychanging at least one of the effective pumping speed of the vacuumchamber and the flow rate of the gas.

In another embodiment, the inventive dry etching method may comprise thesteps of setting the sample in the vacuum chamber, supplying gas to thevacuum chamber, and etching the sample, wherein at least one of theeffective pumping speed of the vacuum chamber and the flow rate of thegas is changed from conditions under which the etching pattern side wallof the sample is formed into a tapered shape, to conditions under whichthe etching pattern side wall is formed in a vertical or undercut shape,or vice versa.

Alternatively, the conditions of the effective pumping speed of thevacuum chamber or the flow rate of the gas, or both, may be changed sothat the shape of the tapered etching pattern side wall of the samplechanges, or so that the number of particles of the gas entering thevacuum chamber may either increase to beyond the predetermined value, ordecrease to beyond the predetermined value. In such a case, thepredetermined value may be determined in accordance with the type ofgas, the conditions for changing gas to plasma, or the material of thesample portion to be etched, or more than one of the above. Moreparticularly, the predetermined value is preferably three times thenumber of particles entering the sample.

In a further embodiment, the dry etching method may include a step ofetching a layer of the sample into a mask pattern, and an overetchingstep for removing etching residue, wherein the effective pumping speedof the vacuum chamber in the overetching step is set higher than that inthe etching step. Further, as before, at least one of the effectivepumping speed of the vacuum chamber and the flow rate of the gas may bechanged from conditions under which a deposit film is produced on theetching pattern side wall of the etched layer in the etching step, toconditions under which no deposit film is produced on the etchingpattern side wall of the etched layer in the overetching step.

In a further embodiment, the intensity of the plasma emission may bemeasured to control at least one of the effective pumping speed of thevacuum chamber and the flow rate of the treated gas in according withthe measured intensity.

Finally, the area of the underlayer exposed by the etching step may bemeasured to control at least one of the effective pumping speed of thevacuum chamber and the flow rate of the gas in accordance with themeasured area.

The invention is further directed to a dry etching apparatus forcarrying out each of the methods set forth above. Thus, the inventivedry etching apparatus preferably includes a vacuum chamber, an inlet forleading gas into the vacuum chamber, and a sample stage for supporting asample to be etched in the vacuum chamber. Means for measuring theintensity of the plasma emission, control means for controlling theeffective pumping speed of the vacuum chamber, control means forcontrolling the flow rate of the gas, and means for controlling at leastone of the two types of control means in accordance with signals fromthe measuring means are preferably also included.

In another embodiment, the invention may include means for measuring thearea of the underlayer exposed by the etching, means for controlling theeffective pumping speed of the vacuum chamber, control means forcontrolling the flow rate of the gas, and control means for controllingat least one of the pumping speed and flow rate control means inaccordance with signals from the measuring means.

In yet further embodiments, during the overall etching process, theeffective exhaust rate in the etching chamber is changed from a firsteffective exhaust rate to a second effective exhaust rate. At this time,the first effective exhaust rate, which is set higher or lower than thesecond effective exhaust rate, may be progressively changed to thesecond effective exhaust rate. The change may occur between main etchingand overetching steps, or may be accompanied by a change in pressure orgas flow rate.

Preferably, when a material that remains at stepped portions after themain etching step—which etches planar portions of the material—is etchedby an overetching step, the effective exhaust rate during theoveretching step is set higher or lower than that of the main etchingstep.

Also, in a process of etching a material made up of two or more layersover a plurality of layers, the effective exhaust rate is changed atleast once.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a)-(d) show timing diagrams illustrating the change in effectivepumping speed, gas flow rate, gas pressure, and percentage of reactionproducts in accordance with elapse of time;

FIG. 2 illustrates the flow of gas particles in a reaction chamber;

FIG. 3 is a diagram of the relationship between total pressure andeffective pumping speed;

FIG. 4 is a diagram showing the relationship between total pressure andpartial pressure of etching gas;

FIG. 5 shows the percentage of etching gas in the reaction chamber;

FIG. 6 shows the partial pressure of etching gas when changing the gasflow rate together with the effective pumping speed;

FIGS. 7(a)-7(e) illustrate a process for manufacturing a semiconductordevice in accordance with an embodiment of the inventive dry etchingmethod;

FIG. 8 is a sectional view of an embodiment of the dry etching apparatusconstructed in accordance with the teachings of the present invention;

FIG. 9 shows the plasma emission intensity change for conventional dryetching;

FIGS. 10(a)-10(c) illustrate the change in area of a layer that isetched immediately before the etching step ends;

FIGS. 11(a)-11(d) illustrate a semiconductor device manufacturingprocess for explaining abnormal side etching;

FIGS. 12(a)-12(b) show the changes of plasma emission intensityresulting from reaction products, and the conductance valve openingdegree in an embodiment of the present invention, versus elapsed time;

FIG. 13 is a sectional view of a dry etching apparatus constructedaccording to the teachings of the present invention;

FIG. 14 shows the change of effective pumping speed versus time in anembodiment of the present invention; and

FIGS. 15(a)-15(b) show the relationship between effective pumping speedand side-wall shape.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, then, when the effective pumpingspeed of the dry etching apparatus is changed, the etchingcharacteristics also change. When other etching conditions are notchanged (i.e., when only the effective pumping speed is changed), theetching characteristics change because of a change in the gas pressure.Etching characteristics also change by simultaneously varying the flowrate of the etching gas so that the pressure is kept constant.

The relationship between the effective pumping speed and the etchingcharacteristics are considered below. With reference to FIG. 2, Q (1/s)is the number of etching gas particles entering the vacuum chamber perunit time and the S (m³/s) is the effective pumping speed of the vacuumchamber. When no etching reaction occurs, the gas pressure P in thevacuum chamber is given by the following equation:

P=kTQ/S  (1)

where k is the Boltzmann constant, and T is the absolute temperature ofthe gas.

When the etching reaction occurs, the pressure in the vacuum chamberdiffers from the value in equation (1). Also, the chamber contains notonly the etching gas, but reaction products from the etching itself.

When analyzing the relationship between the effective pumping speed andthe etching characteristics, the following two points are assumed: (1)the etching gas entering the vacuum chamber is completely consumed bythe etching reaction, and (2) only one type of reaction product isproduced. For example, when the incoming etching gas is chlorine gas,and the chlorine gas is used to etch a silicon substrate, the solereaction product in the vacuum chamber is SiCl₄.

In practice, the primary etchant gas is a halogen atomic gas, and therate-determining step is the supply of the etchant gas. The reactionproducts are stable halides. Therefore, the above assumption isreflected in practice.

The etching speed can thus be determined by the incident flux of theetching gas. The incident flux is itself determined by pressure. Thenumber of incoming etching gas particles per unit area and unit time Γis proportional to the partial pressure of the etching gas P₁ asfollows:

Γ₁=αP₁.  (2)

In this case, α is a constant determined by the following expression,where m₁ is the mass of the etching gas particle:

α={square root over (1/2+L πm₁+L kT)}.  (3)

For a wafer area W, the etching gas consumption is Γ₁W per unit time.The number of etching gas particles per unit time exhausted from anexhaust system provided for the vacuum chamber is P₁S/kT (from equation(1)). Unless the pressure fluctuates, the number of incoming etching gasparticles Q balances the sum of the number of etching gas particlesconsumed during the etching process (Γ₁W) and the number of etching gasparticles exhausted from the exhaust system P₁S/kT. That is,

Q=Γ₁W+P₁S/kT.  (4)

Substituting equation (2) for equation (4), P₁ is obtained as follows:

P₁ =kTQ/(S+αkTW).  (5)

The number of reaction products Γ₂ per unit area and unit time ejectedfrom a wafer is proportional to the number of incoming gas particles Γ₁.That is,

Γ₂ =xΓ ₁.  (6)

For example, when the etching gas particle is a chlorine atom, and thereaction product is SiCl₄, x equals ¼. The number of reaction productsproduced per unit time is Γ₂W. Unless the pressure fluctuates, thenumber of reaction products produced by the etching process equals thenumber of reaction products ejected from the exhaust system.

The number of reaction product particles per unit time ejected from theexhaust system is P₂S/kT, where P₂ is the partial pressure of thereaction products. That is,

Γ₂W=P₂S/kT.  (7)

Then, substituting the equations (2) and (6) for the equation (7), P₂ isobtained as follows:

P₂ =xkTαWP₁/S.  (8)

The relationship between the pressure P in the vacuum chamber, thepartial pressure P₁ of the etching gas, and the partial pressure P₂ ofthe reaction products is given by the following expression:

P=P₁+P₂.  (9)

Substituting the equations (5) and (8) for the equation (9) to eliminateP₁ and P₂, the following expression is obtained:

pS² −kT(Q−αWP)S−x(kT)²αWQ=0.  (10)

This expression shows the relationship between the effective pumpingspeed and the pressure during the etching reaction.

From the equation (10), S is obtained as shown below:

S={(Q−αWP)+{square root over ((Q−αWP)²+4x+L αWPQ)}}kT/2P.  (11)

Accordingly, the effective pumping speed for setting the pressure to apredetermined value can be obtained using equation (11). By substitutingthe value for equation (5), the partial pressure of the etching gas canbe obtained. In the above consideration, all gas particles confrontingthe wafer are assumed to cause the etching reaction. Therefore, theetching speed can be said to be proportional to the partial pressure ofthe etching gas.

The following is a study of the relationship between the effectivepumping speed and etching characteristics. For this example, a chlorineatom gas is used, the reaction product is SiCl₄, and the gas temperatureis set to room temperature.

FIG. 3 shows the relationship between the total pressure P and theeffective pumping speed S when changing only the effective pumping speedwhile keeping the etching gas flow rate constant for a gas flow rate of100 sccm and a 5-inch wafer. The dotted line shows the relationshipbetween the pressure and the pumping speed when no reaction occurs; thatis, when equation (1) is effected. Although the equation (1) is effectedin a low-pressure area when reaction occurs, the pumping speed decreasesin a high-pressure area, because, if the reaction occurs, the number ofgas particles decreases from four (chlorine atoms) to one (SiCl₄).Therefore, the pumping speed should be decreased by a valuecorresponding to the decrease of the number of particles in order tomaintain the pressure.

Equation (1) is effected in the low-pressure area because the number ofetching gas particles entering the vacuum chamber is much greater thanthe number of gas particles consumed by the etching reaction. Therefore,the partial pressure of etching gas rises in the low-pressure area.

FIG. 4 shows the relationship between the total pressure and the partialpressure of etching gas when changing the exhaust speed while keepingthe gas flow rate constant. In FIG. 4, the dotted line represents theetching gas pressure, i.e., P=P₁ when no etching reaction occurs. In thelow-pressure area, the partial pressure of etching gas is responsiblefor almost all of the total pressure.

In the high-pressure area, however, the line for the partial pressure ofetching gas goes downward from the line for P=P₁. This shows that thepartial pressure of reaction products increases; that is, the percentageof reaction products in the gas increases.

FIG. 5 shows the percentage of etching gas. As shown, the etching gascontent is almost 100% of the total gas in the low-pressure area, butdecreases as the pressure increases (as the pumping speed decreases).

Thus, as the pressure rises (as the pumping speed decreases), thepercentage of reaction products in the gas increases. When thepercentage of reaction products increases, re-dissociation of reactionproducts in plasma and reattachment to the wafer occur. The side-wallprotective film produced during the chlorine- or bromine-based gasetching process is formed by the deposition of the etching reactionproducts from the resist and silicon. For the exemplary etching process,a 5-inch wafer is patterned at the gas flow rate of 100 sccm and thepressure of 5 mtorr. FIG. 5 shows that 70% of the gas is used forreaction products.

The amount of deposition from reaction products, however, can becontrolled. To increase the amount of deposition from reaction products,the effective pumping speed is decreased and the percentage of reactionproducts in the gas is increased. To decrease the amount of depositionfrom reaction products, the effective pumping speed is increased and thepercentage of reaction products in the gas decreased. To increase theeffective pumping speed, the value of (Q−αWP) in the right side ofequation (11) is increased. The upper limit (Q−αWP)>>0 represents thatthe number of incoming etching gas particles is larger than the numberof etching gas particles reacting with the wafer. This situationcorresponds to the limit in which equation (1) is satisfied. Thus,almost all of the particles in the chamber are etching gas particles,and deposition from reaction products does not occur.

The limit (Q−αWP)<<0 represents that the number of etching gas particlesentering the wafer is larger than the number of incoming etching gasparticles. At this limit, most particles in the chamber are reactionproducts, and the amount of deposition from reaction products is large.

As described above, the amount of deposition from reaction products isdetermined by the percentage of reaction products in the gas, whichpercentage is determined by the relationship between Q and αWP. Todecrease the amount of deposition from reaction products, the percentageof reaction products is decreased to 20% or less. For the example ofFIG. 5, the percentage of reaction products in the chamber can bedecreased to 20% or less if Q/αWP>3.

For the above example, then, x equals ¼. When x equals 1, equation (11)can be written as shown below.

S=kTQ/P.  (12)

Thus, the equation (1) is satisfied.

When substituting equation (12) for equation (5), the following equationis obtained:

P₁=QP/(Q+αWP).  (13)

The percentage of etching gas P₁/P can be written as shown below:

P₁/P=Q/(Q+αWP).  (14)

Substituting C for Q/αWP, equation 14 can be rewritten as shown below:

P₁/P=C/(C+1).  (15)

In this case, equation (15) shows that the percentage of reactionproduct in the gas decreases to 20% or less; that is, equation (15)shows that the percentage of etching gas becomes 80% or more when C isgreater than four. Thus, when Q/αWP exceeds three or four, no depositionfrom reaction products occurs. However, when Q/αWP is equal to or lessthan three or four, deposition from reaction products occurs.

As described above, reaction product deposition can be controlled simplyby changing the effective pumping speed of a dry etching apparatus.However, when the gas flow rate is fixed, basic etching characteristicsincluding the etching speed also change because the pressure changes. Itis also possible to control reaction product deposition by adjusting thegas flow rate in accordance with the change of the effective pumpingspeed to keep the pressure constant.

FIG. 6 shows the change of the partial pressure of etching gas whenchanging the gas flow rate together with the effective pumping speed sothat the pressure is kept constant at 0.5 mtorr. The example in FIG. 6is calculated with the same system as that of the sample in FIG. 5.

When Q/αWP is larger than three, the chamber is nearly completelyoccupied by etching gas. When Q/αWP is smaller than three, however, thepartial pressure of etching gas decreases. In this case, the percentageof reaction products increases and deposition from reaction productsoccurs. Thus, deposition from reaction products can be controlled bychanging the effective pumping speed even if the gas flow rate issimilarly adjusted to keep the pressure constant.

Moreover, the shape of the side wall can be changed from the undercut orvertical shape due to side etching to the tapered shape by changing theeffective pumping speed to thereby control the amount of deposition fromreaction products.

Time-modulated etching, in which etching and deposition are alternatelyrepeated, is realized by periodically changing the effective pumpingspeed without changing gases.

The amount of reaction product deposition is preferably controlled sothat the thickness of the side-wall protective film around the interfaceis not decreased by decreasing the effective pumping speed in accordancewith a decrease in the etched layer immediately before the end of theetching step. As a result, abnormal side etching around the interfacecan be prevented.

Because a change in the effective pumping speed of a dry etchingapparatus is carried out in accordance with the change of plasmaemission intensity or a change in the specific wavelength of the plasmaemission, the effective pumping speed immediately before the end of theetching step can be controlled while monitoring the percentage ofreaction products in the gas. Further, because the change in theeffective pumping speed can be realized by monitoring the change of thearea where an underlayer appears immediately before the end of theetching step, or by monitoring the change of the area of the etchedlayer, the effective pumping speed immediately before the end of theetching step can be controlled accurately.

Formation of the side-wall protective film caused by deposition fromreaction products plays an important role in the etching ofpolycrystalline silicon and polycide using chlorine or bromine gas.However, it is not necessary to form the side-wall protective filmduring overetching. In accordance with the present invention, theeffective pumping speed is increased during overetching so thatdeposition from reaction products does not occur. As a result, theetching speed is increased and the throughput is improved duringoveretching.

Moreover, because no side-wall protective film is formed on anoveretching portion, isotropic etching is performed and etching residueon a step can effectively be removed. Furthermore, the throughput isimproved because anisotropic etching can be changed to isotropic etchingwithout changing gases.

Embodiment 1

For this embodiment, a resist mask is used to etch polycrystalline Siwith Cl₂ plasma.

A sample structure is shown in FIG. 7(a). Silicon substrate 4 has aone-micron step, on which a SiO₂ film 3 having a thickness of 200 nm isformed as an underlayer before depositing polycrystalline Si layer 2 toa thickness of 500 nm. A resist mask 1 having a thickness of 1.5 μm isthen formed on polycrystalline Si layer 2. By way of example, Sisubstrate 4 is a 5-inch wafer.

Using a Cl₂ gas plasma, etching is carried out at a pressure of 5 mtorrand using a gas flow rate of 100 sccm, the plasma being generated bymicrowave discharge. In this case, the effective pumping speed of a dryetching apparatus is set to 170 l/s. The wafer temperature is set to 10°C., and a 2-MHz RF bias is applied to the Si substrate 4.

Under these conditions, side etching normally occurs. However, when aresist mask is used, side etching is controlled because the side-wallprotective film 5 is formed, as shown in FIG. 7(b). For the etchingconditions outlined above, Q is set to 4.18×10¹⁹ (1/s), αWP is set to2.18×10²⁰ (1/s), and Q/αWP thus equals 0.19. Therefore, the percentageof reaction products is as high as about 80%, and deposition from thereaction products occurs so that side-wall protective film 5 is formedat a vertical portion of the sample. At portions other than the sidewall, deposit is immediately removed because etching progresses withincoming gas and, thus, no deposit film is formed. However, the etchingspeed is decreased compared with the condition in which no depositionfrom reaction products occurs. Thus, for the present etching conditions,the etching speed is 300 nm/min.

FIG. 7(c) illustrates a state in which the etching of thepolycrystalline Si film is completed. Etching residue of polycrystallineSi layer 2 is present on the step side wall because high anisotropicetching is performed by controlling side etching. The overetching stepis thus necessary to remove the etching residue.

For the existing dry etching method, the overetching step conditions arethe same as the etching step conditions, or overetching is performed bychanging gases. For this embodiment, however, overetching is performedby increasing the effective pumping speed.

For the overetching, the gas pressure is set to 0.5 mtorr, the gas flowrate is set to 160 sccm, and the other conditions are set similarly tothose of the etching step previously described. In this case, however,the effective pumping speed is set to 4000 l/s.

For these etching conditions, because Q equals 6.69×10¹⁹ (1/s), αWPequals 2.18×10¹⁹ 1/s, and Q/αWP equals 3.1, giving a percentage ofreaction products of less than 20%. Therefore, because no depositionfrom reaction products occurs, the etching speed increases and isotropicetching progresses. An etching speed of 600 nm/min is obtained, which istwo times the speed of the previous etching step (FIG. 7(d)).

In this case, because the gas pressure is set as low as 0.5 mtorr,incoming ions have a high directivity. Therefore, the side-wallprotective film 5 is only slightly, if at all, etched. Though theside-wall protective film of the etching residue remains for a period oftime, it is eventually removed because the vertical portion of theetching residue disappears when overetching is progressed to a certainextent. Then, isotropic etching subsequently progresses and overetchingcan be performed without leaving the etching residue (FIG. 7(e)).

FIG. 1 shows time charts for the above etching conditions. FIG. 1(a) isa time chart showing the change of the effective pumping speed inaccordance with elapsed time, FIG. 1(b) is a time chart showing thechange of the etching gas flow rate in accordance with elapsed time,FIG. 1(c) is a time chart showing the change of the gas pressure inaccordance with elapsed time, and FIG. 1(d) is a time chart showing thechange of percentage of reaction products. By increasing the effectivepumping speed under overetching, the etching speed under overetching canbe doubled and isotropic etching realized. The overetching time can thusbe decreased to one-half or less than the existing overetching time.

As a result, it is possible to prevent a short circuit from occurringdue to a very small amount of etching residue. Also, because thepercentage of carbon in plasma resulting from the resist decreases inthe overetching step, the selectivity for the SiO₂ layer 3 greatlyincreases, and etching with small damage can be performed.

The present embodiment describes polycrystalline Si etching usingchlorine plasma and a resist mask. The present invention is effectivefor every type of etching using a side-wall protecting film andrequiring overetching. For example, it is also effective for the“Cl₂+O₂” etching with an oxide film mask, etching of polycide, etchingwith a bromine-based gas plasma, and etching of metals includingaluminum and tungsten.

Embodiment 2

FIG. 8 shows a dry etching apparatus representing another embodimentconstructed according to the teachings of the present invention. Thisapparatus introduces an etching gas into a vacuum chamber 19, generateselectromagnetic wave radiation of 2.45 GHz with a microwave generator17, and sends the electromagnetic wave radiation to the vacuum chamber19 through a waveguide 18 and a microwave entrance window 14 to generatea gas plasma with the etching gas. For high-efficiency discharge,solenoid coils 15 are arranged around vacuum chamber 19 to generate thehigh-density plasma through electron cyclotron resonance using amagnetic field of 875 gauss. The vacuum chamber 19 contains a samplestage 16 on which a wafer 6 is set to be etched with the gas plasma.

The etching gas is lead into the vacuum chamber 19 through a gas supplyport 7, which may be covered with a mesh, or may be provided with smallholes, through a gas pipe 11, gas flow rate controller 10, and bufferchamber 12. The etching gas is exhausted from the vacuum chamber 19 byexhaust pump 8. In this case, the pumping speed can be changed via aconductance valve 9.

Because a buffer chamber 12 is provided, and because the gas releasingarea is increased by the structure of gas supply port 7, the velocity ofgas can be decreased to one-third or less than the speed of sound, and auniform flow is realized. Moreover, two or more gas supply ports 7 maybe arranged so that they are symmetric with respect to the central axisof the vacuum chamber 19 to lead the gas from the gas pipe 11 to thevacuum chamber 19. This structure thereby makes possible the control ofthe bias of the gas distribution in the plasma gas.

The sample stage 16 is equipped with an RF power source 13 so that an RFbias of 400 kHz to 13.56 MHz can be applied. If the sample stage 16includes a cooling system and a heating system, etching can beinfluenced by controlling the wafer temperature.

Plasma emission from the gas plasma is received by a light receivingapparatus 22 to determine the spectrum of the plasma emission. Lightreceiving apparatus 22 is operably associated with a photoemissionspectroscope and photodetector jointly represented by reference numeral20. The photoemission spectroscope and photodetector 20 detects spectrahaving a specific wavelength, and converts light intensity intoelectrical information to be sent to a batch control unit 21. Thephotoemission spectroscope and photodetector 20 can measure not onlyspectra having a specific wavelength, but the light intensity of theentire plasma emission.

Batch control unit 21 further controls the operation of conductancevalve 9. In accordance with the construction described above, theeffective pumping speed of the dry etching apparatus can be controlledin accordance with the change of plasma emission intensity.

FIG. 9 shows how the emission intensity resulting from reaction productschanges for the conventional dry etching apparatus. The emissionintensity resulting from the reaction products is kept constant duringthe etching step, and then slowly decreases immediately before the endof the etching step because the area of the layer 25 to be etcheddecreases slowly, and the underlayer 26 begins to appear, as shown inFIG. 10. The time for the emission intensity to begin this decrease (t₁in FIG. 9) corresponds to the time for the layer to start disappearingwhen the etching speed is maximized (FIG. 10(a)). When the emissionintensity is approximately half (t₂ in FIG. 9), the area of the layer isalso approximately half (FIG. 10(b)). When the layer 25 is completelyetched (FIG. 10(c)), the emission intensity resulting from reactionproducts all but disappears (t₃ in FIG. 9). However, overetching isstill necessary because etching residue of the layer remains on the sidewall.

When the area of layer 25 decreases as shown in FIG. 10(b), the amountof reaction products also decreases. As a result, the amount ofdeposition from the reaction products decreases. Therefore, thethickness of the side-wall protective film decreases. This state isshown in FIG. 11.

FIG. 11(a) shows the structure whereby underlayer 26 has been depositedon Si substrate 4, layer 25 has been deposited on underlayer 26, andmask 27 has been formed on layer 25. The state immediately before theend of the etching step is shown in FIG. 11(b). As shown, the side-wallprotective film 5 has been formed on the pattern side wall. Where a highetching speed is present (the left side of FIG. 11(b)), the amount ofreaction products is kept constant until the underlayer appears.Therefore, the side-wall protective film 5 is adequately formed up tothe interface. At a portion having a low etching speed (right side ofFIG. 11(b)), however, the area of layer 25 decreases, as shown in FIG.10(b). Therefore, the thickness of the side-wall protective film 28decreases around the interface with the underlayer 26 (right side ofFIG. 11(c)). Thus, the side-wall protective film 28 is broken underoveretching, and the abnormal side-etching portion 29 is easily producedat the interface as shown in FIG. 11(d).

Since the amount of reaction products in the gas can be maintained bydecreasing the effective pumping speed in accordance with a decrease ofthe production of reaction products, the thickness of the side-wallprotective film 5 can be maintained. The dry etching apparatus describedin this embodiment makes it possible to monitor the emission intensityresulting from reaction products, and to control the effective pumpingspeed in accordance with the emission intensity. Therefore, thethickness of the side-wall protective film does not decrease, so that noabnormal side etching occurs.

FIGS. 12(a) and 12(b) illustrate an example of effective pumping speedcontrol. The conductance valve 9 is slowly closed in accordance with adecrease in emission intensity resulting from reaction products ofapproximately one-half immediately before the end of the etching step sothat the emission intensity resulting from reaction products is keptconstant. In this period, the thickness of the side-wall protective film5 can be prevented from decreasing because the amount of deposition fromreaction products is kept constant.

When the layer to be etched has been completely etched, the emissionintensity resulting from reaction products starts decreasing even if theconductance valve is almost closed. Then, it is possible to open theconductance valve to begin the overetching step. However, because theeffective pumping speed has already been decreased, the etching speedalso decreases. Therefore, the emission intensity does not decrease fora considerable time.

For this embodiment, however, the conductance valve 9 is opened at thebeginning of the overetching step by assuming that the timing when theconductance valve has closed up to 90% is the end point of the etchingstep, in order to improve throughput. Thus, the thickness of theside-wall protective film 5 can be prevented from decreasing, andabnormal side etching does not occur, by decreasing the effectivepumping speed immediately before the end of the etching step whilemonitoring the emission intensity.

Depending upon the etching conditions, abnormal side etching may notoccur even if overetching begins when the conductance valve is up to 80%closed, or it may occur by the time the overetching step begins afterthe conductance valve is closed up to 90% or more. Therefore, to furtheraccurately control the effective pumping speed, the area of the layer orthe area of the exposed underlayer is monitored instead of monitoringthe emission intensity. FIG. 13 shows an embodiment of thisconstruction.

The embodiment shown in FIG. 13 incorporates a video camera 23 and imageprocessor 24 in place of the light receiving apparatus 22 and thephotoemission spectroscope and photodetector 20 of the dry etchingapparatus illustrated in FIG. 8. The change in area of the layer 25being etched is monitored by camera 23 immediately before the end of theetching step, which area is converted into electrical information by theimage processor 24 and sent to batch control unit 21. By adjusting theeffective pumping speed in accordance with the change in area of theetching layer and of the underlayer, the thickness of the side-wallprotective film can be kept constant and the abnormal side etching canbe prevented.

The effective pumping speed can further accurately be adjusted bycombining this embodiment with the monitoring method using the plasmaemission intensity. For example, while adjusting the effective pumpingspeed so that the plasma emission intensity becomes constant immediatelybefore the end of the etching step, the timing for starting theoveretching step can accurately be determined by monitoring the timethat the layer disappears with the camera system.

Embodiment 3

Time modulation etching, in which depositing and etching gases arechanged by turns, can be performed with one type of gas by using thecharacteristic that deposition from reaction products occurs or does notoccur depending on the effective pumping speed. For this embodiment,shown in FIG. 14, the effective pumping speed is periodically changed at170 l/s and 4000 l/s when polycrystalline Si is etched with Cl₂ plasmausing a resist mask. When the effective pumping speed is 170 l/s, thepressure is set to 5 mtorr, the gas flow rate to 100 sccm, and the watertemperature to 10° C. In this case, deposition from reaction productsoccurs. When the effective pumping speed is 4000 l/s, the gas pressureis set to 0.5 mtorr, and the gas flow rate is set to 160 sccm. In thiscase, the etching speed increases and isotropic etching progressesbecause no deposition from reaction product occurs.

As just described, the time modulation etching in which deposition andetching are periodically repeated can be performed with only one type ofgas, and accurate etching free from the micro loading effect isrealized.

Embodiment 4

The percentage of reaction products can be changed by changing theeffective pumping speed. Therefore, because the deposition speed can becontrolled, it is possible to control the taper angle for taperedetching in accordance with the effective pumping speed.

FIG. 15 shows an example of the relationship between the effectivepumping speed and the side-wall shape. The characteristics shown in FIG.15 is for etching of polycrystalline Si on a 5-inch wafer with a resistmask and Cl₂ microwave plasma at a pressure of 5 mtorr and wafertemperature of 10° C.

Under these conditions, αWP equals 2.18×10²⁰ (1/s). Therefore, whenincreasing the effective pumping speed so that gas flows at a rate of Qequals 6.54×10²⁰ (1/s), which is three times larger than αWP equals2.18×10²⁰, or 1600 scam, an undercut shape is formed due to side etchingbecause no deposition from reaction products occurs. When decreasing theeffective pumping speed, then, the amount of side etching is decreaseddue to the effect on deposition from reaction products, and side etchingdoes not occur at the gas flow rate of 200 sccm. When further decreasingthe effective pumping speed, the amount of deposit increases due todeposition from reaction products, and a taper angle starts to appear.At a gas flow rate of 10 sccm, the taper angle is 70 degrees. Therefore,the side-wall shape can be controlled by changing the effective pumpingspeed.

Moreover, a structure in which an upper portion of a side wall isapproximately vertical, a middle portion has a tapered angle, and abottom portion is approximately vertical can be obtained by repeatingthe etching with the same conditions as just outlined, except that thegas flow rate is changed from, for example, 200 sccm to 10 sccm to 200sccm.

Embodiment 5

This embodiment is generally directed to the proposition that, duringthe etching process, the effective exhaust rate in the etching chamberis changed from a first effective exhaust rate to a second effectiveexhaust rate, the first effective exhaust rate thus being higher orlower than the second effective exhaust rate. In a more particularembodiment, the effective exhaust rate may be progressively changed fromthe first effective exhaust rate to the second effective exhaust rate.

The reason for changing the effective exhaust rate during etching isthat the thickness of the side-wall protective film produced by thereaction product also changes. As the amount of reaction productdecreases, the thickness of the side-wall protection film may becomeinsufficiently small, resulting in side etching. As the amount of thereaction product increases, however, the side-wall protection filmbecomes thicker, with the result that the processed geometry of theside-wall protection film has a taper, lowering the etch rate.

Thus, when the reaction product amount decreases, the effective exhaustrate should be reduced during the etching process to prolong the timethat the reaction product stays in the chamber, allowing the sideprotection film of the reaction product to be readily formed, therebysuppressing the side etching. Conversely, when the reaction productincreases, the effective exhaust rate should be increased during theetching process to shorten the time that the reaction product stays inthe chamber, inhibiting the production of the side-wall protection filmand thereby preventing the processed geometry from being tapered. Thus,high-speed etching that minimizes the reduction in etching rate ispossible.

By progressively changing the effective exhaust rate between the firstand second rates, the uniformity of thickness of the side-wallprotection film can be ensured. This is important to maintaininganisotropy of the etch in the face of the phenomenon that the area ofmaterial being etched changes as a result of the material being removedfrom the surface of the wafer by the etching process. For example, in apolysilicon gate forming process, because the thickness of thepolysilicon layer and the etch rate do not have a perfectly linearrelationship, the etching area of the polysilicon layer progressivelydecreases immediately before the end of the etching. At the same time,the amount of reaction product generated also progressively decreases.Thus, by progressively changing the effective exhaust rate in accordancewith the amount of reaction product generated, the thickness of theside-wall protection film can be more accurately controlled.

Embodiment 6

In the process of forming polysilicon gates on stepped portions, afterplanar portions of the polysilicon layer have been etched down throughthe thickness of the polysilicon layer in the main etching step, thepolysilicon remaining on the stepped portions is removed in anoveretching step. When the main etching step is performed by lowtemperature etching without using the side-wall protection film,abnormal side etching may occur during the overetching step. In such acase, the effective exhaust rate is reduced during the overetching stepto form the side-wall protection film, thus enabling anisotropic etchingwith no abnormal side etch.

If the side-wall protection film is formed during the main etching step,there is no need to produce the side-wall protection film in theoveretching step. In this case, the effective exhaust rate is increasedin the overetching step to realize high-speed overetching that minimizesthe influence of the reaction product.

Embodiment 7

When a material to be etched consists of a plurality of layers, theamount of reaction product generated during etching may differ from onelayer to another. In a layer that produces a large amount of reactionproduct, the etch rate increases when the exhaust rate is increased,while in a layer which produces only a small amount of reaction product,the etch rate may fail to increase even if the exhaust rate isincreased. Thus, when etching two or more such layers in one sequence,the effective exhaust rate is preferably reduced when etching a layerthat produces a small amount of reaction product in order to reduce theetch rate of a mask without lowering the etch rate of the material to beetched, thereby improving the selectivity of the etching.

Embodiment 8

When the effective exhaust rate in the etching chamber is set to 800liters/second or higher, it is possible to suppress the formation of theside-wall protection film made from the reaction product, and to performa high-speed etching that minimizes a reduction in the etch rate causedby the reaction product. The higher the effective exhaust rate, thebetter the effect of the reaction product can be suppressed. Butconsidering the size of the equipment, the effective exhaust rate mustnot exceed 100,000 liters/second.

On t he contrary, when the effective exhaust rate is set to 700liters/second or lower, the time that the reaction product stays in thechamber becomes long, and the side-wall protection film will form. Inother words, as the effective exhaust rate is reduced, the influence ofthe reaction product increases. It is noted that when the effectiveexhaust rate is lower that 1 liter/second, a problem arises that thecontrol of the exhaust rate becomes difficult.

By changing the effective exhaust rate from 800-100,000 liters/second to1-700 liters/second or from 1-700 liters/second to 800-100,000liters/second during the etching process, it is possible, even duringthe etching process, to select between the high-speed processing, whichsuppresses the influence of the reaction product, and the side-wallprotection process using the reaction product, thereby etching with highspeed and good anisotropy.

Embodiment 9

During overetching, the area of the material being etched decreases, sothat the amount of reaction product generated decreases. Although theside-wall protection film is formed even at the effective exhaust rateof 700 liters/second, it is preferred that the effective exhaust rate isset lower than 500 liters/second to form a stronger side-wall protectionfilm. Hence, by changing the effective exhaust rate between 1-500liters/second and 800-100,000 liters/second, it is possible during theoveretching to select between the high-speed processing, whichsuppresses the influence of the reaction product, and the side-wallprotection process using the reaction product, thus allowing high-speedetching with good anisotropy.

Embodiment 10

At an effective exhaust rate of more than 1,300 liters/second, thereaction product generated is exhausted at high speed to increase theamount of etching species supplied and thereby suppress the phenomenon(microloading) in which the etch rate decreases with the aspect ratio.When the effective exhaust rate is lower than 700 liters/second, thetime in which the reaction product stays in the chamber becomes long,enabling the side-wall protection film to form. Therefore, by changingthe effective exhaust rate between 1,300-100,000 liters/second and 1-700liters/second, it is possible to suppress the microloading and at thesame time obtain an etching geometry that prevents side etching by usingthe side-wall protection film.

Embodiment 11

As noted, during overetching, the processing area of the material beingetched and the amount of reaction product generated both decrease. Atthis time, if the effective exhaust rate is set to less than 500liters/second, the side-wall protection film can be formed to asufficient thickness during the overetching. At an effective exhaustrate of more than 1,300 liters/second, the reaction product is exhaustedat high speed to increase the amount of etching species supplied tosuppress the microloading phenomenon, in which the etch rate decreaseswith the aspect ratio. Therefore, by switching the effective exhaustrate between 1,300-100,000 liters/second and 1-500 liters/second, it ispossible to perform overetching without microloading, while suppressingthe side etch by forming the side-wall protection film.

Embodiment 12

By keeping the gas flow constant and changing the pressure between thetwo predetermined values in order to change the effective exhaust rate,it is possible to change between the high-speed processing, whichsuppresses the influence of the reaction product, and the side-wallprotection process using the reaction product, without degradation inthe etching uniformity that might otherwise be caused by changes in gasflow, thereby realizing a high-speed etch with good anisotropy. A gasflow of more than 200 sccm allows high-speed processing that suppressesthe influence of the reaction product. A gas flow of more than 100,000sccm, however, is too great for practical processing.

When the pressure is set below 5 mTorr, the amount of ions striking thewafer at angles decreases, realizing a high anisotropy. However, whenthe pressure is below 0.01 mTorr, the electric discharge becomesunstable. At the other range, at a pressure higher than 10 mTorr, thenumber of neutral particles striking the wafer increases, so that theside-wall protection film is efficiently formed by the reaction product,but a pressure in excess of 1,000 mTorr destabilizes the electricdischarge. Thus, the pressure preferably changes between the ranges of0.01 mTorr-5 mTorr and 10 mTorr-1,000 mTorr.

Embodiment 13

By holding the pressure constant and changing the gas flow in order tochange the effective exhaust rate, it is possible to change between thehigh-speed processing, which eliminates the influence of reactionproduct, and the side-wall protection process using the reactionproduct, without causing variations in the etch rate and selectivitythat may accompany pressure change-induced variations in ion currentdensity and plasma potential. This realizes high-speed etching with goodanisotropy. When the pressure is set between 1 mTorr and 1,000 mTorr, astable electric discharge can be obtained even when the gas flow ischanged. In this pressure range, the use of a gas flow higher than 200sccm offers high-speed processing with no influence of the reactionproduct. A gas flow of more than 100,000 sccm, however, is too great forpractical processing. A gas flow less than 100 sccm results in aside-wall protection process that uses the reaction product, but theetching process requires at least 1 sccm of gas flow.

Embodiment 14

At a pressure less than 4 mTorr, the amount of neutral particlessupplied to the bottom of a pattern with a high aspect ratio isrelatively insufficient for the amount of ions, so that microloading islikely to occur. At a pressure more than 25 mTorr, the proportion ofions striking the pattern at an angle increases, resulting in areduction in the amount of ions reaching the bottom of the pattern witha high aspect ratio, which in turn makes the microloading likely tooccur and causes side etching by diagonally-incident ions. At aneffective exhaust rate of less than 600 liters/second, the etch rate ofSiO₂ is increased by the reaction product from a resist mask containingcarbon atoms, reducing selectivity. Therefore, with a dry etchingapparatus that can be set at an effective exhaust rate of more than 600liters/second and a pressure of 4-25 mTorr, it is possible to perform adry etching having a high selectivity without causing microloading andside etching.

Embodiment 15

When the pressure is below 4 mTorr, the amount of neutral particles atthe bottom of the pattern with a high aspect ratio becomes too small forthe amount of ions, making the microloading likely to occur. At apressure higher than 25 mTorr, the amount of diagonally-incident ionsincreases, so that the amount of ions reaching the bottom of the patternwith a high aspect ratio decreases, making the microloading likely tooccur and causing side etching by the diagonally-incident ions. At aneffective exhaust rate below 600 liters/second, the etch rate of SiO₂ isincreased because of the reaction product from the resist maskcontaining carbon atoms, thus reducing selectivity. Therefore, byperforming dry etching at an effective exhaust rate of more than 600liters/second and a pressure in the 4-25 mTorr range, it is possible toprevent microloading and side etching and obtain high selectivity.

Embodiment 16

Using the low temperature etching technique to suppress side etching,and setting the effective exhaust rate to higher than 800 liters/second,high-speed etching with good anisotropy can be realized without formingthe side-wall protective film during the main etching step that etchesthe planar portions of the material to be processed. In this case,however, abnormal side etching may occur at the boundary between etchedlayer and underlayer during the overetching. Thus, during theoveretching, the effective exhaust rate is set below 700 liters/secondto form a side-wall protection film to prevent abnormal side etching.

Embodiment 17

During overetching, the area of the material being etched decreases,reducing the amount of reaction product generated. In this case, theeffective exhaust rate is set below 500 liters/second to form a solidside-wall protection film to prevent abnormal side etching.

Embodiment 18

As a specific embodiment of the dry etching method performed accordingto several of the Embodiments described above, a polysilicon etching byCl₂ plasma using a resist mask is performed at a gas flow rate of 200sccm and with a pressure charged to 3 mTorr and 10 mTorr alternately.The effective exhaust rate is changed between 850 liters/second and 260liters/second. By changing the pressure in this way, it is possible toetch with good anisotropy at a high etch rate of 600 nm/min whileforming the side-wall protection film by the reaction product.

Embodiment 19

As another specific embodiment of the dry etching method of thisinvention, a polysilicon etching by Cl₂ plasma using a resist mask isdescribed. Etching is performed at a pressure of 2 mTorr by changing thegas flow rate between 200 sccm and 100 sccm alternately, and changingthe effective exhaust rate between 1270 liters/second and 640liters/second. By changing the gas flow alternately in this way, etchingwith good anisotropy and at a high etch rate of 600 nm/min can berealized while forming the side-wall protective film by the reactionproduct.

Embodiment 20

As a further specific embodiment of the dry etching method of thisinvention, a process of continuous etching of a laminated layerconsisting of a TiN layer and an overlying Al layer, that uses a mixtureof a Cl₂ gas and a BCl₃ gas using a resist mask is described. At apressure of 3 mTorr, when the etching is performed on the aluminumlayer, a greater effective exhaust rate results in an increased etchrate; that is, an effective exhaust rate of 600 liters/second achievesan etch rate of 800 nm/min, and 800 liters/second realizes an etch rateof 1,000 nm/min. The total gas flow of the gas mixture at this time is110 sccm for the effective exhaust rate of 600 liters/second and 150sccm for 800 liters/second.

The etch rate of the TiN layer also increases as the effective exhaustrate is increased until it reaches 600 nm/min for an effective exhaustrate of 600 liters/second, after which the etch rate does not rise evenif the effective exhaust rate is further increased. The etch rate of theresist, however, does increase with the effective exhaust rate. An etchrate of 200 nm/min is achieved for the effective exhaust rate of 600liters/second and, for 800 liters/second, the etch rate is 300 nm/min.When etching is done at an effective exhaust rate of 800 liters/second,both the Al layer and the TiN layer can be etched at high rates, 1,000nm/min for Al layer and 600 nm/min for TiN layer. The etch rate of theresist mask during the TiN layer etching is 300 nm/min, producing aTiN/resist selectivity ratio of two.

If the etching of the Al layer is performed at an effective exhaust rateof 800 liters/second while the TiN layer is etched at an effectiveexhaust rate of 600 liters/second, it is possible to etch both of thelayers at high etch rates: 1,000 nm/min for Al and 600 nm/min forTiN—the rates that can be realized when these two layers are etched atthe effective exhaust rate of 800 liters/second. Changing the effectiveexhaust rate in this manner allows the etch rate of the resist to besuppressed to 200 nm/min during the etching of the TiN layer, producinga TiN/resist selectivity ratio of three, and thus realizing a highlyselective etching.

Embodiment 21

As a further specific embodiment of the dry etching method of thisinvention, polysilicon etching by Cl₂ plasma using a resist mask isdescribed. At a pressure of 2 mTorr, etching is performed by changingthe effective exhaust rate between 800 liters/second and 700liters/second. The gas flow is set to 130 sccm and 110 sccm for aneffective exhaust rate of 800 liters/second and 700 liters/second,respectively. By changing the effective exhaust rate alternately duringthe etching, it is possible to form the side-wall protection film whenthe effective exhaust rate is 700 liters/second and, at 800liters/second, to perform a high-speed processing that suppresses theinfluence of the reaction product, thus realizing a high-speed etchingwith good anisotropy, but without side etching.

While this embodiment changes the effective exhaust rate between 800liters/second and 700 liters/second, it is also possible to change itbetween 800 liters/second and 500 liters/second to produce a solidside-wall protection film even when the amount of reaction productgenerated becomes small during the overetching. If the effective exhaustrate is changed between 1,300 liters/second and 700 liters/second, it ispossible to suppress the microloading phenomenon when patterns ofdifferent sizes are processed simultaneously, allowing a high-speed,anisotropic etching. Further, changing the effective exhaust ratebetween 1,300 liters/second and 500 liter/second eliminates themicroloading phenomenon and produces a solid side-wall protection filmduring the overetching, thus realizing the high-speed etching with goodanisotropy.

Embodiment 22

As a further specific embodiment of the dry etching method of thisinvention, polysilicon etching by Cl₂ plasma using a resist mask isdescribed. During the main etching step, the pressure is set at 3 mTorr,the effective exhaust rate at 800 liters/second and the gas flow at 260sccm. The wafer is cooled to −50° C. At this low temperature the sideetching of polysilicon is suppressed, so that good anisotropic etchingis assured even under conditions where the side-wall protection film isnot formed. The effective exhaust rate of 800 liters/second, whicheliminates the influence of the reaction product, allows a high-speedprocessing at the etch rate of 600 nm/min.

In the overetching step, even when the wafer is cooled to as low as −50°C., abnormal side etching is likely to occur at the boundary between thepolysilicon and the underlying SiO₂. To prevent the abnormal sideetching, this embodiment reduces the effective exhaust rate during theoveretching step to 700 liters/second. The pressure is set at 3 mTorrand the gas flow at 230 sccm. With the effective exhaust rate set to 700liters/second during the overetching step, the side-wall protection filmis formed by the reaction product, preventing the abnormal side etching.The etch rate at this time is reduced to 500 nm/min because of theinfluence of the reaction product. Reducing the effective exhaust rateduring the overetching step below 700 liters/second enables theside-wall protective film to be formed. But because, during theoveretching step, the etching area of the polysilicon becomes small,reducing the amount of reaction product generated, it is preferred thatthe effective exhaust rate is set below 500 liters/second to form astronger side-wall protection film. If the effective exhaust rate duringthe main etching step is set to 1,300 liters/second or higher,microloading can be suppressed during the main etching step.

Embodiment 23

As a further specific embodiment of the dry etching method of thisinvention, polysilicon etching by Cl₂ plasma using a resist mask isdescribed. Pressure is set at 10 mTorr, the effective exhaust rate at600 liters/second and the gas flow at 470 sccm. Under these conditions,the etch rate of polysilicon is 500 nm/min and the polysilicon/SiO₂selectivity ratio is 50. The gas flow and the pressure are increased andwhen the pressure exceeds 25 mTorr, the etch rate decreases because of areduction in the ion current density. At 30 mTorr the polysilicon etchrate is halved to 250 nm/min and the gas flow and the pressure arereduced. When the pressure is below 4 mTorr, however, microloadingoccurs due to a lack of etchant supply. Hence, a desirable pressurerange for this process is 4-25 mTorr. When the effective exhaust rate isreduced below 600 liters/second, the polysilicon etch rate decreaseswhile the etch rate of SiO₂ does not fall to a similar extent. This isbelieved to occur due to the carbon atoms in the reaction productaccelerating the etching reaction of SiO₂. At the effective exhaust rateof 500 liters/second, the polysilicon/SiO₂ selectivity ratio is reducedto 10. Therefore, the preferred effective exhaust rate for this processis 600 liters/second or higher.

The advantages of the present invention as outlined above are confirmedby applying the teachings of the invention to the specifically-describedetching apparatus, as well as to other apparatus such as a magnetron RIE(reactive ion etching) apparatus and a helicon RIE apparatus. Moreover,a similar effect occurs by applying the present invention's teachings toother etching materials than those described, such as aluminum,tungsten, tungsten-silicide, copper, GaAs, and silicon nitride films.

The various modifications of the invention described above will becomeapparent to those of ordinary skill in the art. All such modificationsthat basically rely upon the teachings through which the presentinvention has advanced the state of the art are properly consideredwithin the spirit and scope of the invention.

We claim:
 1. A method for manufacturing a semiconductor device havingstorage capacitors, comprising the following steps: providing a bodywhich includes a semiconductor substrate having steps into a chamber;and etching the body in the chamber by using plasma of an etching gas,while exhausting the chamber by using at least one pump; wherein aneffective exhaust speed of the chamber is not less than 600liters/second; and wherein the effective exhaust speed is defined asfollows:${1/S} = {{1\text{/}{\sum\limits_{n}^{\quad}\quad {Si}}} + {1/C}}$

where S is the effective exhaust speed, Si is an exhaust speed of onepump, n is the number of pumps, and C is an exhaust conductance of thechamber.
 2. A method for manufacturing a semiconductor device accordingto claim 1, wherein a gas pressure of the chamber is not more than 25mTorr.
 3. A method for manufacturing a semiconductor device according toclaim 1, wherein a gas pressure of the chamber is not more than 10mTorr.
 4. A method for manufacturing a semiconductor device according toclaim 1, wherein the body is set at a point other than the ECR point. 5.A method for manufacturing a semiconductor device according to claim 1,wherein a reaction product of the body and the etching gas has a qualityof deposition with respect to the body.
 6. A method for manufacturing asemiconductor device according to claim 1, wherein the body has one ofsilicon, aluminum, tungsten, tungsten-silicide, copper, GaAs, siliconnitride and titanium nitride.
 7. A method for manufacturing asemiconductor device according to claim 1, wherein the etching gasincludes Cl or Br.
 8. A method for manufacturing a semiconductor deviceaccording to claim 1, wherein the residence time of the etching gas inthe chamber is not more than 300 msec.
 9. A method for manufacturing asemiconductor device according to claim 1, wherein a conductance of thechamber is not less than 2000 liters/second.
 10. A method formanufacturing a semiconductor device having storage capacitors,comprising the following steps: providing a body which includes asemiconductor substrate having steps into a chamber; and etching thebody in the chamber by using plasma of an etching gas, while exhaustingthe chamber; wherein an effective exhaust speed of the chamber is notless than 600 liters/second; and wherein a conductance of the chamber isnot less than 2000 liters/second.
 11. A method for manufacturing asemiconductor device according to claim 10, wherein a gas pressure ofthe chamber is not more than 25 mTorr.
 12. A method for manufacturing asemiconductor device according to claim 10, wherein a gas pressure ofthe chamber is not more than 10 mTorr.
 13. A method for manufacturing asemiconductor device according to claim 10, wherein the body is set at apoint other than the ECR point.
 14. A method for manufacturing asemiconductor device according to claim 10, wherein a reaction productof the body and the etching gas has a quality of deposition with respectto the body.
 15. A method for manufacturing a semiconductor deviceaccording to claim 10, wherein the body has one of silicon, aluminum,tungsten, tungsten-silicide, copper, GaAs, silicon nitride, and titaniumnitride.
 16. A method for manufacturing a semiconductor device accordingto claim 10, wherein the etching gas includes Cl or Br.
 17. A method formanufacturing a semiconductor device according to claim 10, wherein theresidence time of the etching gas in the chamber is not more than 300msec.
 18. A method for manufacturing a semiconductor device according toclaim 10, wherein the effective exhaust speed of the chamber is not lessthan 800 liters/second.